Measurement of effective focal spot size. Literature divergencies

A brief description of the bar pattern object is presented, followed by the presentation of the mathematical approach to the problem of determining the effective focal spot size, proposed by Gopala U. V. Rao. This work shows three tables, coming from different publications, and a fourth, that comes from the Rao's formula. The four tables relate spatial frequency with focal spot size, and they are supposed to show the same values, but they don't. In order to get some insight into the accuracy of the method originally proposed by Rao, measurements of effective focal spot sizes made up to now in some X-ray machines are also shown. These values are compared with the manufacture's stated values, just to show that the Rao's method is the best approach to the actual focal spot size. (author)